The present invention relates to a seat track structure employed in a seatbelt system for a vehicle designed to protect an occupant in an emergency situation. The seat track structure incorporates a belt anchor for anchoring the seatbelt system to the body of the vehicle.
In general, a seat for an occupant of a vehicle is mounted on the floor of the vehicle body through a seat track comprising a lower rail which is secured to the floor surface, and an upper rail which is secured to the seat and adapted to be slidable on the lower rail. In contrast, the inner belt of the seatbelt system is typically secured directly to the floor of the vehicle body without any relation to the seat track. Therefore, the tension generated in the webbing by the inertia acting on the occupant's body when an emergency situation of the vehicle occurs is directly supported by the floor.
There is another conventional arrangement in which the inner belt is secured to the seat so that the webbing can be fastened to the body of the occupant at a constant position at all times regardless of the occupant's adjusting the position of the seat in the longitudinal direction of the vehicle. With this arrangement, however, when an emergency situation occurs, the seat track is subjected to a large load which acts such as to separate the upper and lower rails from each other. It is therefore necessary to make the seat track more solid.
The lower rail of the seat track is generally bent at the upper edge thereof in the horizontal direction, and the upper rail is mounted on the lower rail in such a manner as to cover this bent portion of the lower rail. Therefore, in order to strengthen the seat track, it is necessary to enlarge the width of the seat track which leads to a reduction in the leg space for the occupant in the rear seat.
To overcome this problem, a structure has been proposed in which, despite the inner belt being secured to the seat, the seat track is not subjected to a large load even when an emergency situation occurs (see, e.g., Japanese Utility Model Laid-Open No. 257/1985). With this arrangement, however, it is necessary to lay a rail and the like on the vehicle body separately from the seat track, resulting in a complicated structure.
The present inventors have proposed a structure in which the seat track is arranged vertically. A load which is transmitted to the seat track from the belt anchor is supported by a retaining means which is movable in the lateral direction of the vehicle and which extends through the seat track, thereby preventing separation of the upper and lower rails (see U.S. application Ser. No. 863,423, filed May 15, 1986).
In this structure, however, the retaining means is disposed below the seat, and this disadvantageously reduces the degree of freedom with which the configuration of the seat cushion frame is designed.